crystalyte motor

It should be fine. Know how many amps your controller is? It's probably higher than the 20A fuse, and that's why it kept blowing it.

What sort of batteries are you using? Why it's cutting out may be due to the BMS initiating its overcurrent protection if it's lithium, I'm not sure what it could be if it's something else. You can charge them whenever if it's not SLA, keep them charged all the time if it is.

Your 48v battery ( you typed niam but i assume nimh ) will be ok with a 40 amp fuse, like Link says, if your controller is a 20, 25, or 40 amp model..

Nimh will self discharge just sitting on the shelf.. if you don't ride daily.. it's best to leave it in what ever state of charge it's in after your ride.. and charge it the night before you plan to use it type thing..

Try not to recharge and already fully charged nimh pack.. depending on the quality of your charger it can overcharge the pack before it shuts down in some cases, not deadly but not good for cycle life ..

If the pack is hot after a ride. let it cool down before you charge it.

Cutting out can be from the controller LVC (* Low voltage cut off ) if the voltage sags bad enough, hook up a volt meter to the charge leads and tape it to the bike so you can see the voltage when you accelerate and report back.

my crysalyte is 48v niam and keeps blowing 20amp fuses,so i put a 40amp in and its ok,will it do any harm?,also when i accelerate it cuts out for a second then starts again,it does this the harder i accelerate,does any one know why?also should i keep my battery fully charged all the time or should i run it flat then charge it?

I don't think it can do any harm. It just needs more current and there is nothing wrong with that. Feel free to use 40amp fuse

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All the best

Andy
Electric Bikes, Electric Bicycles and Ebikes in London UK